Currently, reduction of body weight has been required of automobiles for lowering environmental burdens with satisfying collision safety standards. For achieving both of such safety and weight-saving, with regard to a vehicle skeleton, there has been widely used a method of increasing body rigidity by spot-welding a reinforcing component to an appropriate part of a steel-made structural material subjected to sheet metal working
For achieving further remarkable weight-saving, it has been attempted to apply a carbon fiber composite material that is a more light-weight material to a material for a vehicle skeleton member, instead of steel. However, since the vehicle skeleton member has a complex shape or is extremely large, it is necessary to use an expensive carbon fiber fabric for producing such a member having the carbon fiber composite material. Furthermore, since a shaping technology for a carbon fiber composite material whose matrix component is a thermoplastic resin is not sufficiently established, it is also necessary to perform shaping using a hand lay-up or autoclave method that is low in productivity with the use of a carbon fiber composite material containing a thermosetting resin as a matrix component. As a result, the vehicle skeleton member made of the carbon fiber composite material is very disadvantageous in view of productivity and economical efficiency and thus wide use thereof has been necessarily extremely limited.
Recently, although an improvement in productivity using RTM method (Resin Transfer Molding method) is attempted (for example, see Patent Document 1), length of the time for curing reaction of the thermosetting resin used as a matrix is a serious difficulty in productivity and thus the method has not yet been accomplished as a technology applicable to widely used vehicles.
As a means for improving the productivity of a composite material of a resin and a reinforcing fiber, a thermoplastic composite material using a thermoplastic resin as a matrix component has been developed. Such a thermoplastic composite material enables impartment of a shape within a short tact time by stamping molding after the material is heated and plasticized and, since pressing pressure required for stamping is lower than that for stamping molding of a steel, integral molding is applicable in the case of such a size as a floor for a vehicle. Moreover, it is possible to produce a thermoplastic composite material in which a reinforcing fiber having a form of continuous fiber is aligned in one direction by a pultrusion method.
However, as mentioned above, a vehicle skeleton member is difficult to shape since it has a complex shape and is extremely large and also required levels for safety and strength are extremely high, so that practical one as a vehicle skeleton member having a composite material of a thermoplastic resin and a reinforcing fiber has not been obtained
(Patent Document 1) JP-A-2008-68720